I wish I could answer your question but I'm not sure. I looked at the grill cloths with a bright flashlight and there looks like there's a grove that a fame might fit into but I'm not going to do anything to the speakers to determine if there's a frame or not... I'd be afraid I'd break something if I start poking around or whatever.
Sorry but that's the best i can do here. I could try to photograph the grill cloth at the edge if you're really interested.
G.